Silicon-on-insulator (SOI) is emerging to be a promising platform for dense photonic integration due to the strong light confinement and matured electronics industry. To enable the technology of photonic system on chip, integrating direct band-gap materials/devices on SOI substrate have been investigated and demonstrated recently for light emission, amplification or absorption.
FIGS. 1A and 1B show respectively the cross-sectional view and the side view of a hybrid micro-waveguide structure with III-V bonded on a patterned SOI of the prior art. The hybrid structure 100 includes a SOI micro-waveguide 102 and a III-V direct-band semiconductor 104. The SOI micro-waveguide 102 may include or consist of a patterned silicon core layer 106 with a bottom cladding of silicon dioxide 108. The direct-band semiconductor 104 on the top of the SOI micro-waveguide 102 may include or consist of an n-contact layer 110, a core region 112 and a top p-cladding 114.
The direct-band semiconductor 104 is bonded on the SOI micro-waveguide 102. Appropriate width and height of the silicon waveguide (e.g. of the silicon core 106) are chosen so that the hybrid micro-photonic waveguide structure 100 confines the light in the silicon waveguide in the central region (as schematically shown in FIG. 1A in the shaded circle 120) but amplifies/absorbs through the evanescent field confined in the bonded III-V semiconductor material 104. FIG. 1B illustrates the confinement of light, as represented by 122, in the SOI micro-waveguide 102 and the propagation of the light 122 through the silicon core 106 of the SOI micro-waveguide 102. In addition, FIG. 1B illustrates that the evanescent field of the light 122, as illustrated in the dotted circle 124, extends to the direct-band semiconductor 104, to be absorbed by the core region 112.
In other conventional structures, the direct-band semiconductor is bonded on a low-refractive index material (e.g. Benzocyclobutene, BCB) and the light is coupled to the waveguide (e.g. polymer waveguide) fabricated surrounding the SOI waveguide through butt-coupling.
These configurations have some shortcomings in terms of silicon nanophotonic integration applications, such as efficiency, size, thermal management, and fabrication complexity, etc.